apostrophe - How to use possessives when the subject has a number after?

I have a question about possessives.

While "Peter's ball" is easy and clear.

How do I express the notion of "the ball that belongs to agent 2"?

Would it be "agent's 2 ball" or "agent 2's ball" or what else?

Answer

Your second guess is correct:

Agent 2's ball

The ball is owned by 'agent 2', which is a noun phrase. You should put the apostrophe indicating possession after the complete noun phrase, regardless of whether the noun phrase includes numbers or not.

You can see this form when referring to royalty:

King Henry V's advisors

or to government and military organizations:

Directorate 7's responsibilities